1. Technical Field of the Invention
This invention relates to a semiconductor device having a circuit configured with thin film transistors (hereinafter, referred to as TFTs) and a method for manufacturing the same, e.g. an electro-optical device represented by the liquid crystal display panel and an electronic apparatus mounted with such an electro-optical device as a part.
Incidentally, in the description, the semiconductor device refers to the device overall operable by making use of a semiconductor property, wherein the electro-optical device, the semiconductor circuit and the electronic apparatus, in any, are a semiconductor device.
2. Description of the Related Art
Recently, development has being proceeded for the semiconductor device that thin film transistors (TFTs) are configured with using a semiconductor film (in a thickness of nearly several to several hundred nm) formed on a substrate having an insulating surface thus having a large-area integrated circuit formed with the TFTs. The known representative examples include active-matrix liquid crystal modules, EL modules and contact-type image sensors. Particularly, the TFT using a crystalline silicon film (typically a polysilicon film) in an active layer (hereinafter, described polysilicon TFT) is high in electric-field mobility and allowed to form various functions of circuits.
For example, the liquid-crystal module mounted on a liquid-crystal display device has pixel-circuit-controlling driver circuits, such as a pixel circuit for image display based on a function block, a shift register circuit on the basis of CMOS circuits, a level shifter circuit, a buffer circuit and a sampling circuit, formed on one substrate.
Meanwhile, the pixel circuit of an active-matrix liquid crystal module has TFTs (pixel TFTs) respectively arranged in several tens to several millions of pixels wherein each pixel TFT has a pixel electrode. The counter substrate, sandwiching liquid crystal, has a counter electrode to form a kind of capacitor using a liquid crystal as dielectric. The voltage to be applied to each pixel is controlled by TFT switching function to control the charge onto the capacitor, thereby driving the liquid crystal and hence controlling transmission light amount for image display.
The TFT electric characteristic is ready to be influenced by the channel region in the neighborhood of an interface between a semiconductor and a gate insulating film. The present invention provides TFTs reduced in electric characteristic deviations and a method for manufacturing the same.